Stacked semiconductor package and stacking method thereof

ABSTRACT

A stacked semiconductor package technique applicable to semiconductor chips having pins short enough that the semiconductor chips cannot be directly bonded together is provided. A printed circuit board (PCB) is inserted into a space between pins of an upper semiconductor chip and the exterior of bodies of stacked semiconductor chips. The PCB includes a plurality of conductive patterns at locations corresponding to the respective pins. The respective conductive patterns and the corresponding respective pins of the upper and lower semiconductor chips are bonded together. The PCB includes a plurality of recess patterns on one side, the recess patterns having the same pitch as the pins of the semiconductor chips. The PCB is disposed across the pins of the lower semiconductor chip, and thereby easily arranged with the stacked semiconductor chips.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a division of U.S. patent application Ser. No.12/954,489, filed on Nov. 24, 2010, now U.S. Pat. No. 8,310,041 whichclaims the benefit under 35 U.S.C. §119(a) of Korean Patent ApplicationNo. 10-2010-0077986, filed on Aug. 12, 2010, the entire disclosure ofwhich is incorporated herein by reference for all purposes.

BACKGROUND

1. Field

The following description relates to a stacked semiconductor packagetechnique for stacking semiconductor chips on a chip basis.

2. Description of the Related Art

A new stacked semiconductor package technique that doubles memorycapacity by, for example, stacking two identical memory semiconductorpackages has been introduced. U.S. Pat. No. 6,242,285 discloses a methodthat has been implemented by an applicant of the present invention. Theabove prior art is advantageous in its implementation since pins on anupper chip are deformed and subsequently are directly bonded with pinson a lower chip.

However, some pins have been recently designed to have shorter lengths,so that ends of pins on an upper chip come to be relatively far apartfrom upper ends of pins on a lower chip. Consequently, after a solderingpaste process, bonding is performed improperly, resulting in theoccurrence of more defects.

SUMMARY

The following description relates to a technique for effectivelystacking chips having shorter pins. A complex technique for easily andeffectively connecting pins spaced apart from each other by a distancethat makes the pins impossible to be directly bonded together isprovided.

In one general aspect, provided is a stacked semiconductor packageincluding: a first semiconductor chip configured to comprise a pluralityof first pins on at least one side for connection with an externalcircuit; a second semiconductor chip configured to be stacked above thefirst semiconductor chip and comprise a plurality of second pins on atleast one side corresponding to the first pins, the second pins havingends that extend toward and are spaced apart from upper portions of thecorresponding first pins; a printed circuit board (PCB) configured to bedisposed in a space between the second pins and chip bodies of the firstand second semiconductor chips and along a length of the first andsecond semiconductor chips and comprise a plurality of conductivepatterns, each extending from the end of the corresponding is second pintoward the upper portion of the corresponding first pin; and a pluralityof bonding portions, each configured to electrically connect aconductive pattern of the PCB, an end of a corresponding second pin andan upper portion of a corresponding first pin.

The PCB may be further configured to comprise a plurality of recesspatterns on one side, each recess pattern having the same pitch as thefirst pin. The PCB may be arranged in alignment with the first andsecond semiconductor chips by the recess patterns in contact with theupper portions of the corresponding first pins.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side view illustrating an example of an exterior of aprinted circuit board (PCB).

FIG. 1B illustrates a cross-sectional view taken along a line C-C′ inthe example illustrated in FIG. 1A.

FIG. 1C is an enlarged view illustrating an example of the stackedsemiconductor package shown in the example illustrated in FIG. 1A.

FIG. 1D is an enlarged cross-sectional view illustrating an example of arecess pattern and a first pin and a second pin being bonded together.

FIG. 2 is an enlarged view illustrating another example of a recesspattern of a PCB and first and second pins being bonded together.

FIG. 3 illustrates a flowchart of an example of the method of stackingsemiconductor chips.

Throughout the drawings and the detailed description, unless otherwisedescribed, the is same drawing reference numerals will be understood torefer to the same elements, features, and structures. The relative sizeand depiction of these elements may be exaggerated for clarity,illustration, and convenience.

DETAILED DESCRIPTION

The following description is provided to assist the reader in gaining acomprehensive understanding of the methods, apparatuses, and/or systemsdescribed herein. Accordingly, various changes, modifications, andequivalents of the methods, apparatuses, and/or systems described hereinwill be suggested to those of ordinary skill in the art. Also,descriptions of well-known functions and constructions may be omittedfor increased clarity and conciseness.

FIG. 1A is a side view illustrating an example of an exterior of aprinted circuit board (PCB) and its pins before a stacked semiconductorpackage passes through soldering paste. FIG. 1B is a cross-sectionalview taken along a line C-C′ in the example illustrated in FIG. 1A. FIG.1C is an enlarged view illustrating an example of the stackedsemiconductor package shown in the example illustrated in FIG. 1A. FIG.1D is an enlarged cross-sectional view illustrating an example of arecess pattern and a first pin and a second pin being bonded together.

As shown in FIGS. 1A to 1D, the stacked semiconductor package mayinclude a first semiconductor chip 100 and a second semiconductor chip200 which is stacked on the first semiconductor chip 100. The firstsemiconductor chip 100 may include a plurality of first pins 110-1, . .. , and 110-10 on a side for connection to an external circuit. Thesecond semiconductor chip 200 may include a plurality of second pins210-1, . . . , and 210-2 on a side. As shown in the example illustratedin FIG. 1B, ends of the second pins 210 are spaced apart fromcorresponding upper portions of the first pins 110 and extend upward.

In a space between the second pins 210 and chip bodies 170 and 270, thePCB 300 is is disposed above the first pins 110 along a length of thefirst and second chips 100 and 200. The PCB 300 may include a pluralityof conductive patterns 310-1, . . . , and 310-10 that correspond to thefirst and second pins. The conductive patterns 310-1 to 310-8 and310-10, excluding a conductive pattern 310-9 that is formed to beshorter than the rest, are designed to extend from the ends of thecorresponding second pins 210 to the upper portions of the first pins110. The conductive patterns 310-1 to 310-8 and 310-10 are electricallyconnected to the ends of the corresponding second pins 210-1 to 210-8and 210-9 and the upper portions of the corresponding first pins 110-1to 110-8 and 110-10 by a bonding portion 500.

As shown in FIGS. 1A to 1D, similar to the prior art, in the stackedsemiconductor package, the ends of the second pins 210 are deformed toextend toward the upper portions of the first pins 110. However, thepresent invention is not limited to the above, and may include asemiconductor chip having pins originally extending downward. Unlike theprior art, the ends of the second pins 210 are not long enough to reachthe upper portions of the first pins 110. Soldering in accordance withthe prior art cannot provide reliable electrical connection between theends of the second pins 210 and the upper portions of the first pins110. The conductive patterns 310 formed on the PCB offer an extendingplane that allows soldering paste to be stably connected between the endof the second pins 210 and the upper portions of the first pins 110. Inthe example, the bonding portion 500 may be formed by soldering thefirst and second pins 110 and 210 and the conductive patterns 310. Inthe course of passing through soldering paste solution, solderingsolution is adhered to cover the upper portions of the first pins 110,passing through the conductive patterns 310 from the ends of the secondpins 210, and thereby providing stable electrical connection between thefirst and second pins 110 and 210.

Although U.S. Pat. No. 6,242,285 discloses a method of connecting pinsusing an auxiliary unit similar to a PCB, the PCB of the prior art onlyprovides a path for bridging is between a control pin on an upper chipand a no-connection (NC) pin on a lower chip. A configuration forbridging is not particularly disclosed in the prior art. According tothe above prior art, the pins on the upper and lower chips are directlyconnected primarily by soldering.

In the examples illustrated in FIGS. 1A to 1D, the PCB 300 may be aflexible PCB (FPCB), or may be any other type of PCB. In anotherexample, the PCB 300 may include a plurality of recess patterns 330having the same pitch as the first pins 110 on a side. The recesspatterns 330 are in contact with the upper portions of the respectivefirst pins 110, and thus the PCB 300 can be aligned with the first andsecond pins 110 and 210 of the respective first and second semiconductorchips 100 and 200.

In the example, each of the recess patterns 330 may be formed by cuttinga conductive through hole along a length direction, wherein theconductive through hole is in conduction with the conductive pattern310. In this case, since a recess on a cut portion of each recesspattern 330 has a conductive pattern formed thereon, as shown in theexample illustrated in FIG. 1D, the soldering paste permeates deep intothe recess, thereby fastening the connection with the pins 110 and 210.However, the recess patterns 330 may not be limited to the above, andmay be simple patterns without conductive pattern formed thereon.

In another example, the PCB 330 may further include a bridge pattern 350having one end connected to a control pin 210-9 of the secondsemiconductor chip and the other end connected to an NC pin 110-9 of thefirst semiconductor chip. The bridge pattern 350 may be formed on aninner layer so as to be disconnected from the conductive patterns 310-7to 310-9. That is, in this case, the PCB is a multi-layer FPCB.

The illustrated examples are disclosed under the assumption that twoidentical DRAM packages are stacked to double the capacity of memory asan example. However, the described is examples are only exemplary, andare not intended to limit the scope of the present invention. In theexamples, most pins such as address pins and data pins on the respectiveupper and lower chips are connected to the respective correspondingpins. To double the capacity, addresses have to be substantiallyextended by use of a chip select (CS) pin 210-9 which distinguishes thechips from each other during read and write operations. To this end, anNC pin 110-7 on the first semiconductor chip 110 which is a lower chipis used. To connect the CS pin 210-9 to the NC pin 110-7, the bridgepattern is provided.

As shown in the example illustrated in FIG. 1C, the bridge pattern 350may include one end connected to the short conductive pattern 310-9 viaa through hole 351-2 and the other end connected to one 330-7 ofconductive patterns via a through hole 351-1, and be configured as aninner pattern 353 formed on the inner layer of a multi-layer. In thiscase, the short conductive pattern 310-9 is formed on an upper surfaceof the PCB 300 to have a length short enough to be bonded to only one210-9 of the second pins. The conductive pattern 310-9 is formed to beshort enough, and the second pin 210-9 which is bonded to the shortconductive pattern 310-9 is cut substantially short. Hence, in thecourse of passing through soldering paste solution, the solderingsolution covers the first pin 110-9 corresponding to the second pin210-9, and consequently direct electrical connection between the firstpin 110-9 and the second pin 210-9 can be avoided. Accordingly, the CSpin 210-9 on the second semiconductor chip 200 is allowed to beelectrically connected to the NC pin 110-7 on the first semiconductorchip 100, so that the second semiconductor chip 200 can be directlycontrolled through the NC pin 110-7 on the first semiconductor chip 100when the first pins on the first semiconductor chip 100 are connected toan external mount board.

FIG. 2 is an enlarged view illustrating another example of a recesspattern of a PCB and first and second pins being bonded together. Thesame elements as those shown in the is examples illustrated in FIGS. 1Ato 1D have the same reference numerals.

In the example illustrated in FIG. 2, the first semiconductor chip 100and the second semiconductor chip 200 have the same shapes as thoseshown in the example illustrated in FIG. 1A, and they are stacked oneach other, being bonded together. Hereinafter, another example of astacked semiconductor package will be described with reference to FIGS.1A to 1C and FIG. 2. The stacked semiconductor package shown in theexample illustrated in FIG. 2 is formed by stacking the secondsemiconductor chip 200 on the first semiconductor chip 100. The firstsemiconductor chip 100 may include a plurality of first pins 110-1, . .. , and 110-10 formed on one side for connection with an externalcircuit. The second semiconductor chip may include a plurality of secondpins 210-1, . . . , and 210-10 formed on one side. Ends of therespective second pins 210 extend toward upper portions of therespective first pins 110 at a distance. That is, the second pins 210may have been originally designed to have the same shape as the firstpins 110, and then deformed to have the lower ends extending downward.Soldering in accordance with a prior art cannot provide reliableelectrical connection between the ends of the second pins 210 and theupper portions of the first pins 110.

In a space between the second pins 210 and chip bodies 170 and 270, aPCB 300 is disposed above the first pins 110 along a length of the firstand second semiconductor chips 100 and 200. The PCB 300 may include aplurality of conductive patterns 310-1, . . . , and 310-10 correspondingto the first and second pins 110 and 210. The conductive patterns 310-1,. . . , 310-8, and 310-10, excluding a short conductive pattern 310-9,are formed to extend from the ends of the second pins 210 toward theupper portions of the first pins 110. The conductive patterns 310-1, . .. , 310-8, and 310-10 and the ends of the corresponding second pins210-1, . . . , 210-8, and 210-10 and the upper portions of thecorresponding first pins 110-1, . . . , 110-8, and 110-10 areelectrically connected by a bonding portion 500.

In the example illustrated in FIG. 2, the PCB 300 has a front surfacesimilar to that of the PCB 300 shown in the example illustrated in FIG.1C, and they are different from each other in that a rear surface of thePCB 300 of FIG. 2 has a similar pattern to the front surface. In theexample illustrated in FIG. 2, the PCB 300 is an FPCB, but may be anyother type of PCB. As shown in FIG. 2, each conductive pattern 310 ofthe PCB 300 includes a first conductive pattern 311 formed on a surfaceof the PCB 300 facing the chip bodies 170 and 270 and a secondconductive pattern 313 formed on an opposite surface of the PCB 300facing the second pins 210. A plurality of first conductive patterns 311are formed at locations corresponding to the first pins 110. A pluralityof second conductive patterns 313 are formed at locations correspondingto the respective second pins 210. Here, the conductive patterns whichare formed at locations corresponding to the pins are arranged at thesame intervals as the pins and have sizes which correspond to the sizesof the pins and are suitable to be bonded with the corresponding pins.The conductive patterns on the rear surface of the PCB 300 are formed inthe same manner as the example illustrated in FIG. 1C, except for ashort pattern related to a bridge pattern. However, the patterns on therear surface do not need to reach the second pins 210, and thus it isacceptable for the patterns to be short patterns with a short lengthconnected to the conductive patterns formed on the recess patterns 330.In addition, a conductive pattern on the rear surface which correspondsto the conductive pattern 330-9 connected to the CS pin 210-9 isremoved.

Unlike the prior art, the end of the second pin 210 is not long enoughto reach the upper portion of the first pin 110. Soldering in accordancewith the prior art cannot provide reliable electrical connection betweenthe end of the second pin 210 and the upper portion of the first pin110. The conductive pattern 310 formed on the PCB 300 offers an extendedplane that allows soldering paste to be stably connected between the endof the second pin 210 to be connected and the upper portion of the firstpin 110.

In the example illustrated in FIG. 2, the bonding portion 500 may beformed by soldering the first and second pins 110 and 210 to theconductive pattern 310. In the course of passing through soldering pastesolution, soldering solution is adhered to cover the upper portion ofthe first pin 110, passing through the conductive pattern 310 from theends of the second pins 210, and thereby providing stable electricalconnection between the first and second pins 110 and 210.

Although the above mentioned U.S. Pat. No. 6,242,285 discloses a methodof connecting pins using an auxiliary unit similar to a PCB, the PCB ofthe prior art only provides a path for bridging between a control pin onan upper chip and an NC pin on a lower chip. A configuration forbridging is not particularly disclosed in the prior art. In the priorart, the pins on the upper and lower chips are directly connectedprimarily by soldering.

In the example illustrated in FIG. 2, the PCB 300 is an FPCB, but may beany other type of PCB. The conductive pattern 310 of the PCB 300includes the first conductive pattern 311 formed on the surface of thePCB 300 facing the chip bodies 170 and 270 and the second conductivepattern 313 formed on an opposite surface of the PCB 300 facing thesecond pins 210. A plurality of first conductive patterns 311 are formedat locations corresponding to the first pins 110. A plurality of secondconductive patterns 313 are formed at locations corresponding to therespective second pins 210. Here, the conductive patterns which areformed at locations corresponding to the pins are arranged at the sameintervals as the pins and have sizes which correspond to the sizes ofthe pins and are suitable to be bonded with the corresponding pins.

As shown in the example illustrated in FIG. 2, the bonding portion 500may include a first bonding portion 510 which connects the firstconductive pattern 311 and the corresponding first pin 110 on the firstsemiconductor chip 100 and a second bonding portion 520 which connectsthe second conductive pattern 313, the corresponding second pin 210extending from the second semiconductor chip 200 toward the upperportion of the first pin 100, and the upper portion of the first pin100. In comparison with the example illustrated in FIG. 1D, the firstbonding portion 510 is further provided, and thus more reliableelectrical connection between the first and second pins 110 and 120 canbe achieved. As will be described later, while passing through thesoldering paste solution, soldering solution is fixed and bonded to theconductive pattern 310.

According to another aspect, the PCB 300 may further include recesspatterns 330 formed above the upper portion of the first pins 110 and inalignment with the first pins 110 and/or the second pins 210. The recesspatterns 330 may be in contact with the upper portions of the respectivefirst pins 110, and accordingly the PCB 300 can be disposed in alignmentwith the first and second pins 110 and 210 of the first and secondsemiconductor chips 100 and 200.

Each of the recess patterns 330 may be formed by cutting a conductivethrough-hole along a length direction, wherein the conductivethrough-hole electrically connects a first conductive pattern 110 and asecond conductive pattern 210 at a corresponding position. In this case,since a recess on a cut portion of each recess pattern 330 has aconductive pattern formed thereon, as shown in the example illustratedin FIG. 2, the soldering paste permeates deep into the recess, therebyfastening the connection with the first and second pins 110 and 210.However, like in the example illustrated in FIG. 1C, the recess pattern330-9 corresponding to the short conductive pattern 310-9 is a chamferpattern that does not include the conductive pattern. However, therecess patterns are not limited to the above, and all recess patternsmay be simple chamfer patterns without having conductive patterns formedthereon.

According to another aspect, the PCB 300 may further include the bridgepattern 350 that has one end connected to a control pin of the secondsemiconductor chip 200 and the other end connected to the NC pin of thefirst semiconductor chip 100. The bridge pattern 350 may be formed onthe inner layer to be electrically disconnected from the conductivepatterns 310. That is, the PCB 300 in the example illustrated in FIG. 2is a multi-layer FPCB.

The illustrated examples are disclosed under the assumption that twoidentical DRAM packages are stacked to double the capacity of memory.However, the described examples are only exemplary, and are not intendedto limit the scope of the present invention. In the examples, most pinssuch as address pins and data pins on the respective upper and lowerchips are connected to the respective corresponding pins. To double thecapacity, addresses should be substantially extended by use of a CS pin210-9 which distinguishes the chips from each other during read andwrite operations. To this end, the NC pin 110-7 on the firstsemiconductor chip 110 which is a lower chip is used.

As shown in the example illustrated in FIG. 1C, the bridge pattern 350may include one end connected to the short conductive pattern 310-9 viathe through hole 351-2 and the other end connected to one 330-7 ofconductive patterns via a through hole 351-1, and be configured as aninner pattern 353 formed on the inner layer of the multi-layer. Theconductive pattern 310-9 is formed to be short enough, and the secondpin 210-9 which is bonded to the short conductive pattern 310-9 is cutsubstantially short. Hence, in the course of passing through solderingpaste solution, the soldering solution covers the first pin 110-9corresponding to the second pin 210-9, so that direct electricalconnection between the first pin 110-9 and the second pin 210-9 can beavoided. Accordingly, the CS pin 210-9 on the second semiconductor chip200 can be electrically connected to the NC pin 110-7 on the firstsemiconductor chip 100, and hence the second semiconductor chip 200 canbe directly controlled through the NC pin 110-7 on the firstsemiconductor chip 100 when the first pins 110 on the firstsemiconductor chip 100 are connected to an external mount board.

Hereinafter, an example of a method of stacking semiconductor chips willbe described with reference to FIG. 3. FIG. 3 illustrates a flowchart ofan example of the method of stacking semiconductor chips. Pins of thesemiconductor chips are deformed to extend downward (100). If the pinsof the semiconductor chips extend horizontally as the first pins 110 ofthe first semiconductor chip 100 in FIG. 1A, the pins are pressed usinga press mold such that ends of all pins extend downwards. The press moldis formed of a pair of upper and lower molds. When a chip placed on thelower mold is pressed by the upper mold, the ends of the pins aredeformed to be directed downwards. In this case, the control pin 210-9may be processed in advance by a different press mold to be cut shorterthan the other second pins.

Thereafter, the semiconductor chip having the deformed pins is stackedon another semiconductor chip (S200). Referring to FIG. 1A or 2 again,after an adhesive material such as epoxy is applied on a top surface ofthe chip body 170 of the first semiconductor chip 100, the secondsemiconductor chip 200 is pressed upon the first semiconductor chip 100and heat is applied to harden the epoxy, and thereby the twosemiconductor chips 100 and 200 are stacked together. During stackingoperation, a jig may be used to accurately align the first and secondsemiconductor chips 100 and 200.

Then, in a space between the pins of the stacked semiconductor chips andthe exterior of unit chip packages, a PCB including a plurality ofconductive patterns which correspond to at least some pins is disposedin alignment with the pins (300). As shown in the example illustrated inFIG. 1A or 2, to accurately and precisely insert the multi-layer FPCBinto such a narrow space, a microscope may be used to magnify the space.In this case, the PCB may include recess patterns arranged on upperportions of the pins on the lower semiconductor chip.

The conductive patterns, the pins on the upper semiconductor chip, andthe pins on the lower semiconductor chip are electrically connected bybonding (400). To remove impurities from a portion to be bonded, thestacked semiconductor chip packages pass through flux. Subsequently, thestacked semiconductor chip packages pass through a container which isfilled with boiling soldering paste solution up to a constant height,while sinking into the soldering paste solution. The depth for thestacked semiconductor chip packages to sink may be deliberately set toremain at a level that is slightly above the bonding portion between thefirst pins and the second pins. That is, the soldering paste solution isprovided up to a level that is higher than a bonding surface between theupper and lower chips and is lower than a portion of the upper chip fromwhich the pins protrude. Then, the soldering paste solution is cooled tobe hardened, and then passes through a cleaning room to remove residualflux.

A final package after the stacking operation undergoes tests, and thenis packed in a tray for transport.

As described above, when an upper semiconductor chip and a lowersemiconductor chip which are spaced apart such that upper and lower pinsof the respective upper and lower semiconductor chips cannot be directlybonded together are stacked on each other, a PCB including a pluralityof conductive patterns is arranged near the upper and lower pins,thereby allowing reliable bonding between the upper and lower pins.Recess patterns formed on one side of the PCB to have the same pitch asthe pins are placed above upper portions of the lower pins, therebyfacilitating the alignment of the PCB.

The current embodiments can be implemented as computer readable codes ina computer readable record medium. Codes and code segments constitutingthe computer program can be easily inferred by a skilled computerprogrammer in the art. The computer readable record medium includes alltypes of record media in which computer readable data are stored.Examples of the computer readable record medium include a ROM, a RAM, aCD-ROM, a magnetic tape, a floppy disk, and an optical data storage.Further, the record medium may be implemented in the form of a carrierwave such as Internet transmission. In addition, the computer readableis record medium may be distributed to computer systems over a network,in which computer readable codes may be stored and executed in adistributed manner.

A number of examples have been described above. Nevertheless, it will beunderstood that various modifications may be made. For example, suitableresults may be achieved if the described techniques are performed in adifferent order and/or if components in a described system,architecture, device, or circuit are combined in a different mannerand/or replaced or supplemented by other components or theirequivalents. Accordingly, other implementations are within the scope ofthe following claims.

What is claimed is:
 1. A method of stacking a semiconductor chip, themethod comprising: deforming pins of a first semiconductor chip suchthat ends of the respective pins extend downward; stacking and bondingthe first semiconductor chip having the deformed pins onto a secondsemiconductor chip; disposing a printed circuit board (PCB) in a spacebetween the deformed pins of the first semiconductor chip and bodies ofthe stacked first and second semiconductor chips, the PCB comprising aplurality of conductive patterns corresponding to at least some pins ofthe stacked first and second semiconductor chips; and electricallyconnecting the respective conductive patterns and respectivecorresponding pins of the first semiconductor chip and the secondsemiconductor chip.
 2. The method of claim 1, wherein the disposing ofthe PCB comprises disposing the PCB such that recess patterns formed onone side of the PCB are arranged above the pins of the secondsemiconductor chip.
 3. The method of claim 1, wherein the electricalconnecting of the conductive patterns and the pins comprises passing thestacked first and second semiconductor chips through soldering pastesolution which is provided up to a level that is higher than a bondingsurface between the first and second semiconductor chips and is lowerthan a portion of the first semiconductor chip from which the pinsprotrude.